The invention relates to a three-way catalyst with outstanding catalytic activity and aging stability for the cleaning of the exhaust gases of internal combustion engines.
Three-way catalysts are used in large numbers for the cleaning of the exhaust gases of internal combustion engines operated under essentially stoichiometric conditions. They are capable of converting the three significant pollutants from the engine, specifically hydrocarbons, carbon monoxide and nitrogen oxides, simultaneously to harmless components. Frequently, double-layer catalysts are used, which enable a separation of different catalytic procedures and hence an optimal balance of the catalytic effects in the two layers. Catalysts of this kind are described, for example, in EP 0 885 650 and EP 1 046 423.
Double-layer catalysts have the disadvantage that their production is more expensive than that of single-layer catalysts. Moreover, double-layer catalysts have a tendency to an increased exhaust gas backpressure compared to single-layer catalysts, which is at the expense of the performance of the internal combustion engines and the fuel consumption thereof. There have therefore always been efforts to obtain the good catalytic properties of double-layer catalysts by means of single-layer catalysts, as far as possible without tradeoffs. Single-layer three-way catalysts are known, for example, from WO 98/09726, EP 1 138 382 and EP 1 541 220.
The constantly rising demands on reducing the emissions of internal combustion engines necessitate constant further development of the catalysts with regard to catalytic activity, aging stability and production costs. It was therefore an object of this invention to provide a catalyst which has further-reduced lightoff temperatures and improved thermal stability coupled with lower production costs compared to the prior art catalysts.